I agree with DeathAndTaxes on this one. It's not worth trying to limit hardware because it's improving all the time. By the end of this year Intel is expected to release their new Knights Corner 50-core CPU. That will be a good one for mining Litecoins, according to Artforz on btc-e. Are you going to try and stifle that one too?

Do you have any hopes of Litecoin ever becoming mainstream? It won't happen while 50% of the mining is done by botnets! That's why the Litecoin price is so low: nobody is going to put any serious money into a botnet currency.

A GPU miner is the best thing that could happen to LTC because botnets don't have GPUs. Let's leave Litecoin as it is and let's get mtrlt to release an open source version of his miner. I read that he spent only a few hours working on it so the Litecoin community should be able to buy it from him. I'm willing to donate 10 BTC towards this goal.

For proof of work, Bitcoin uses the highly parallelizable SHA256 hash function, and therefore Bitcoin mining is a GPU-friendly task. Litecoin uses scrypt instead of SHA256 for proof of work. The scrypt hash function uses SHA256 as a subroutine, but it also depends on fast access to large amounts of memory rather than depending just on fast arithmetic operations, so it is hard to run many instances of scrypt in parallel by using the ALUs of a modern graphics card. This means that currently CPU mining is more efficient than GPU mining for Litecoin. In the future, GPUs or other dedicated hardware might prove useful for Litecoin mining, though the improvement over CPUs is likely to be less significant than it was for Bitcoin mining (e.g. 4x speedup instead of 400x speedup).

If your computer already mines bitcoins, then the CPU on that computer is probably idle, so you can simultaneously mine litecoins without affecting the speed in which your GPU mines bitcoins.